The objective of the proposed work is to investigate what role changes in intracellular Ca2 ion play in determining the permeability of the soma membrane of neurons. Changes in intracellular Ca2 ion concentration will be measured form changes in the absorbance of arsenazo III injected inside cells in the abdominal ganglion of the gastropod mollusc Aplysia californica. Changes in intracellular pH will be measured from changes in the absorbance of internal phenol red and changes in intracelllular Na ion activity will be measured with Na ion specific electrodes. The effects of changes in internal Ca2 ion on Ca2 ion influx, measured from isolated Ca2 ion currents in nystatin-Cs ion loaded cells, will be investigated. The relation between the rise in intracellullar Ca2 ion, produced by internal Ca2 ion injection or by membrane depolarization, on the Ca2 ion activated K ion conductance willl be determined. The relation between Ca2 ion influx, Ca2 ion sequestration, metabolism and pH will be evaluated. We plan to concentrate our efforts on the effects of change in internal Ca2 ion on membrane K ion permeability during pacemaker and during post-synaptic activity. The long-term goal of this research is to arrive at a more complete understanding of how the receptive membrane of the neuron's soma-dendrite complex integrates incoming information under normal and abnormal (disease-related) conditions.